1. Field of the Invention
The present invention relates to a device for clamping a rotary tool element which is mounted on a spindle of an electric power driven tool or a pneumatic tool such as a portable grinder.
2. Description of the Prior Art
A conventional device for clamping a rotary tool element of a power driven tool is shown in FIG. 5 and has a first flange 8A and a second flange 9A. The first flange 8A is fitted on a spindle 4A and is rotatable with the spindle 4A. The second flange 9A is screwed on the spindle 4A. In a mounting operation of a rotary blade 7A on the spindle 4A, the rotary blade 7A is fitted on the spindle 4A with its one end surface abutting on the the first flange 8A. The second flange 9A is thereafter screwed on a threaded portion 6A of the spindle 4A and is tightened to abut on the other end surface of the rotary blade 7A. Thus, the rotary blade 7A can be removably clamped between the first flange 8A and the second flange 9A.
With the conventional clamp device, however, since the rotary blade 7A is only simply clamped between the fixed first flange 8A and the movable second flange 9A through tightening of the second flange 9A screwed on the threaded portion 6A of the spindle 4A, the rotary blade 7A clamped between the first flange 8A and the second flange 9A may be slided or rotated by the load applied thereto during machining operation of a work in the same direction as that for fastening the second flange 9A. Thus, through the frictional force between the rotary blade 7A and the second flange 9A, the second flange 9A is further tightened to increase the clamping force.
Meanwhile, in order to change the rotary blade 7A, the second flange 9A is loosened and removed from the spindle 4A. Here, the force (torque) for loosening the second flange 9A is influenced by the frictional force between the second flange 9A and the spindle 4A produced at the threaded portion 6A, and that between the second flange 9A and the rotary blade 7A as well as that between the rotary blade 7A and the first flange 8A. Therefore, in the cutting operation of a work made especially of relatively hard material such as a brick, substantial load is applied to the rotary blade 7A, resulting in that the second flange 9A is firmly tightened. This may cause the rotary blade 7A to be worn out earlier. Meanwhile, the second flange 9A normally includes a plurality of holes for engagement with pins of a wrench which is normally attached to this kind of power driven tool , and the second flange 9A is tightened or loosened through rotation by the wrench. However, in case of loosening of the second flange 9A which is hardly tightened as described above, the rotation of the second flange 9A is frequently difficult. Further, if the wrench is compulsorily rotated, the pins or the wrench may be damaged or the holes of the second flange 9A for engagement with the pins may be deformed or enlarged to cause unreliable engagement with the pin, and consequently the device cannot be used further. Additionally, in case a lock device is provided to selectively prevent rotation of the spindle 4A for ease of loosening of the second flange 9A, the lock device and a gear housing on which the lock device is mounted are damaged by the compulsive rotation of the second flange 9A.